bearisgray

For starters, I would also "assume" that the fabric only had 40 inches usable width.

Are you planning to have it long-armed? How much "extra" will you need?

If I was doing the backing and needed 5-inches extra all around, I would buy 5-2/3 yards of fabric and would have leftovers.

I would also wash it before cutting it.

But I just checked - and you live in Canada where fabric is more expensive (usually) than in the USA.

I don't remember if you are in the wash before cutting group or not -

Anyway - I have found some fabrics have shrunk over two inches in width - some have shrunk over two inches in length - very very few that have not shrunk at all.